Myocarditis is inflammation of the heart muscle (myocardium). The inflammation of the heart muscle causes degeneration or death of heart muscle cells. Myocarditis has many different causes and can result in a range of outcomes from mild (presenting briefly and resolving) to rapidly progressing fatal disease. It is differentiated from pericarditis because pericarditis is inflammation of the sac that surrounds the heart and does not involve heart muscle as myocarditis does. However, it is not unusual to have a patient present with both pericarditis and myocarditis.
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Pathophysiology
The virus damages myocardial cells, which triggers an immune reaction. This can cause the destruction of other myocardial cells or cause cross-reactions between viral and myocardial structures, which produce antibodies. This eventually leads to the inability of the heart to pump properly, resulting in heart failure (viral myocarditis).
Types of Myocarditis
Fulminant Myocarditis
Classical clinical triad is the quick onset of symptoms (usually within 2 weeks), compromised hemodynamic properties and fever. High cytokine production is present and biopsy shows inflammation /necrosis in multiple foci. Even if severe global ventricular dysfunction is identified in echocardiography, minimal dilatation is also noted in the ventricle. This condition can be reversed with early diagnosis and aggressive support treatment (high dose vasopressor agent or ventricular assist device); disease may spontaneously resolve.
Giant Cell Myocarditis (Pernicious myocarditis)
It is related to an auto-immune disease, thymoma, and high degree cardiac block. Giant Cell Myocarditis presents histologically with active inflammation and giant cells (with fusion and multi-nucleus) and progressive heart disease are observed. Prognosis is poor and 1-year mortality is 80% with a mean survival rate of 6 months. Recurrence is possible in the transplanted heart.
Chronic Active Myocarditis
This constitutes the major portion of the adult patients and usually starts insidiously, manifesting clinical symptoms consistent with moderate ventricular dysfunction. Biopsy shows active myocarditis; however, borderline or generalized chronic myopathic changes may also accompany fibrosis.
Eosinophilic Myocarditis
It may be due to various reasons and may be secondary to the direct toxic effect of eosinophilic granules. Eosinophilia might not present in the blood. It may develop in drug-induced myocarditis regardless of the period of administration or cumulative dose. Endocardial and valvular fibrosis or endocardial thrombus may be seen. Acute necrotizing eosinophilic myocarditis is the aggressive form of eosinophilic myocarditis with a high mortality rate.
Autoimmune related myocarditis
It is defined as myocarditis secondary to Churg-Strauss syndrome, sarcoidosis, and systemic lupus erythematous. Autoimmune-related myocarditis is generally resistant to medical treatment.
Risk factors
Risk factors include:
- Viral infections: Coxsackie, Influenza, Rubella, Polio, Adeno, and HIV have all been implicated
- Bacterial infections with agents such as Corynebacterium, Rickettsia, Chlamydia, and Coxiella
- Protozoal infections: Trypanosoma Cruzi which causes Chagas’ disease and is common in South America and Toxoplasma Gondii are both known to cause myocarditis
- Radiation and poisoning can cause myocarditis (agents such as lead)
- Rarely, autoimmune processes may cause myocarditis
Myocarditis causes
There are many possible causes (see below), but the most common cause is a viral infection.
Viral infections such as the viruses that cause the common cold, flu, chickenpox, glandular fever, German measles, gastrointestinal (stomach infections and adenovirus lung infections)
Bacterial infections such as Staphylococcus (sometimes called staph infections), Streptococcus (sometimes called ‘strep infections’) and the bacteria that causes Lyme disease (transmitted by ticks)
Fungal infections such as molds, yeasts, and fungi
Allergic reactions to medication such as some antibiotics and anti-epileptic drugs or recreational drugs (such as cocaine)
Reactions to chemicals, radiation or radiotherapy such as some cancer treatments
Immune conditions such as Giant cell myocarditis (a very rare condition where some cells in the heart grow abnormally big). This can be associated with autoimmune conditions where the immune system is overactive and attacks healthy cells and organs such as lupus.
It may not be possible to confirm the exact cause of myocarditis. When a cause can’t be found, this might be referred to as idiopathic (or unknown) myocarditis.
Myocarditis symptoms
One of the greatest challenges to the diagnosis and treatment of myocarditis is its lack of specific symptoms. In many cases, individuals experience no symptoms at all. When they are present, symptoms may point to the viral infection itself or suggest other cardiac problems such as a heart attack. Common symptoms can include but are not limited to:
- Shortness of breath, especially after exercise or when lying down
- Fatigue
- Heart palpitations
- Chest pain or pressure
- Lightheadedness
- Swelling in the hands, legs, ankles, and feet
- A sudden loss of consciousness
If any of these symptoms are detected, it’s important to speak to your doctor right away.
Complications
Severe myocarditis can permanently damage your heart muscle, possibly causing:
Heart failure: Untreated, myocarditis can damage your heart’s muscle so that it can’t pump blood effectively. In severe cases, myocarditis-related heart failure may require a ventricular assist device or a heart transplant.
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